The present invention relates to a compressor system and a method for starting up the compressor system in which an auxiliary burner is used to drive a turbine, and a compressor is driven by the turbine to supply compressed air to the auxiliary burner when the compressor system is started up.
A compressor system of this kind is used to efficiently recover the exhaust gas energy of an air utilizing system without wasting it.
A fuel cell power plant system has the advantages that its efficiency is high in comparison with that of a conventional steam power plant and that it does not pollute the environment as much. A fuel cell power plant comprises a fuel cell body having electrodes of air and fuel and a layer of electrolyte, a reformer for reforming a hydrocarbon fuel such as natural gas and supplying a hydrogen gas as fuel to the fuel cell body, and a compressor system for supplying air to the fuel cell body and the reformer. The performance of the fuel cell body is improved as the pressures of the reacting gases increase. Therefore, the operating pressures of the reacting gases are commonly maintained within a range of 4 to 6 kg/cm.sup.2. The compressor system comprises a turbine receiving the combustion exhaust gas from the reformer and the surplus air from the air electrode of the fuel cell body, and a compressor coaxially connected to the turbine to supply compressed air to the air utilizing system having the fuel cell body and the reformer. The exhaust gas energy is thus collected within the plant system, improving the efficiency of the plant system.
In such a fuel cell power plant system, it is necessary to start up the compressor system when the plant system is started up. However, since the exhaust gas as a driving source cannot be obtained at the initial stage, it is necessary to start up the compressor system by introducing energy from an external source.
A method for solving the above problem is disclosed in Japanese Patent Application No. 59-16685. FIG. 1 shows a compressor system disclosed therein. A fuel cell system 1 comprises a fuel cell body, a reformer and a burner. A compressor assembly 2 comprises a turbine 2a and a compressor 2b coaxially connected to the turbine 2a. The compressor 2b supplies compressed air to the fuel cell system 1 through an air supply conduit 5 in which a regulating valve 6 is disposed to adjust the air flow therethrough.
When the compressor assembly 2 is started up, a change-over valve 4 in an air suction conduit 3 and the regulating valve 6 are closed. A change-over valve 14 in an air inlet conduit 13 is opened to supply air to the compressor 2b, and a regulating valve 10 in a burner conduit 8 is opened to supply compressed air to an auxiliary burner 9. At point in time A of FIG. 2, compressed air is supplied to the compressor 2b through the air inlet conduit 13 by a compressed air supply apparatus 12. The compressed air is then supplied to the auxiliary burner 9, and fuel is supplied from a fuel supply conduit 11 to the auxiliary burner 9. Then, the auxiliary burner 9 is ignited at point in time B to burn the mixture of fuel and compressed air, and the combustion gas is supplied to the turbine 2a. As the temperature of the combustion gas increases, its pressure increases and the compressor assembly 2 is started up at point in time C. When the temperature of the combustion gas has reached a predetermined operating temperature for the turbine 2a, the change-over valve 4 is opened, the operation of the compressed air supply apparatus 12 is stopped at point in time D, and the change-over valve 14 is closed. This state is a stand-by state, and in this state, compressed air can be supplied to the fuel cell system 1 by the compressor 2b at any time when necessary, by opening the regulating valve 6. Exhaust gas generated by the fuel cell system 1 is sent to the turbine 2a through an exhaust gas conduit 7.
In another conventional system such as the system disclosed in Japanese Laid-Open Patent Publication No. 58-12268, a conduit communicating with the atmosphere and having a regulating valve disposed along it is connected to the air supply conduit 5. The regulating valve serves to maintain the pressure of the air on the outlet side of the compressor 2b at a constant level irrespective of changes in the load applied to the fuel cell system 1.
In such a conventional system, after the auxiliary burner 9 has been ignited at point in time B, the compressor assembly 2 is started at point in time C by the energy of the exhaust gas from the auxiliary burner 9. However, such a system has the disadvantages that the combustion of the auxiliary burner 9 is not stable and the auxiliary burner 9 tends to be extinguished. Namely, to improve the combustion efficiency of the auxiliary burner 9, the exhaust gas generated by the combustion in the body of the auxiliary burner 9 is directly supplied to the turbine 2a through the exhaust gas conduit 7, and when the compressor assembly 2 is started up, the air pressures in the air supply conduit 5, the burner conduit 8, and the exhaust gas conduit 7 rapidly increase in a short time which may be less than a few seconds. Accordingly, the pressure in the auxiliary burner 9 rapidly increases during the combustion of the mixture so that the combustion of the combustion burner becomes unstable and the combustion burner tends to be extinguished. Therefore, the conventional system has the disadvantages that the running of the compressor assembly 2 cannot be kept stable during start-up. Furthermore, in this system, when the operation of the compressed air supply apparatus 12 is stopped and the compressor assembly 2 begins running on its own without an external source of compressed air, the pressure of the compressed air on the outlet side of the compressor 2b temporarily decreases which decreases the output power of the turbine and reduces the rotational speed of the compressor assembly. Accordingly, this system also has the disadvantages in that the operation of the compressor assembly 2 is not stable during start-up.